1. Technical Field
A photoresist composition having a low light absorbance to a light source of a wavelength of less than 200 nm is disclosed. More specifically, a VUV (vacuum ultraviolet) photoresist composition comprising TIMD (tetraisopropyl methylene diphosphonate) is disclosed that lowers a light absorbance to a light source of a wavelength of 157 nm.
2. Description of the Related Art
A photoresist composition used for a VUV photoresist film needs to have a low light absorbance at a wavelength of 157 nm, an excellent etching resistance, an ability to be adhesively attached to a wafer, and an ability to be developed with standard 2.38 wt % or 2.6 wt % aqueous TMAH (tetramethylammonium hydroxide) solutions.
Recently, much research has been conducted on resins having a high transparency at a wavelength of 193 nm and the same etching resistance as that of novolack resin which is a photoresist resin for KrF. However, since most of these photoresist resins show a high light absorbance at a wavelength of 157 nm, these photoresist resins are not suitable for a VUV photoresist film.
In order to overcome the above-described problem, research on a photoresist resin containing fluorine and silicon has been conducted. Unfortunately, polyethylene or polyacrylate resins containing fluorine have weak etching resistance, low solubility in the TMAH aqueous solution which results in degradation in development of the photoresist film, and poor adhesive property to a silicon substrate. Additionally, the compounds containing fluorine are gaseous at room temperature due to their low boiling point, and they should be handled with care because of their strong toxicity.
On the other hand, photoresist resins containing silicon have an etching process which is required to have the two-step treatment with hydrofluoric acid-oxygen. It is therefore difficult to completely remove fluorine after the treatment process.
In addition, photoresist resins containing silicon have an outgassing phenomenon where gas is generated in an exposure process, thereby damaging lens of a scanner or a stepper. In other words, silicon gasified by the exposure reacts with air to be transformed into SiO2. When the SiO2 is deposited on lens, a method for removing the SiO2 has not been suggested yet, and expensive lens of the scanner or the stepper must be replaced frequently.
Although polyethylene or polyacrylate resins containing fluorine having excellent solubility to developing solution may be used for VUV photoresist films, these resins still have poor etching resistance and adhesive property to a substrate, and high light absorbance.